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Buy potato chips in London and a number on the bag will tell you its carbon footprint equals 75 grams of carbon emissions. That label serves two excellent functions: it renders transparent the ecological impact of those chips, and lowers the cognitive cost to zero of learning that impact.

Such carbon footprint ratings, in theory, allow shoppers to favor products with better impacts, and companies to do the same with their operations. Well and good. Except the footprint concept, intended to mobilize the mass changes we need, ignores fundamentals of human motivation, tending to stifle change, not encourage it.

It's time we moved beyond talking about "carbon footprints", replacing the concept with a more precise measure of all the negative impacts of a given human activity on planetary systems for sustaining life. And while we're at it, let's go easy on the very idea of any kind of 'footprints'—the numbers are demoralizing. There's a more motivating replacement waiting in the wings: Handprints.

First, the expanded footprint. While the dialogue on global warming and its remedies focuses tightly on the carbon impact of our activities and energy systems—as measured by their carbon footprint—this very focus skews the conversation.

Technically a carbon footprint represents the total global warming impact of greenhouse gas emissions from a given activity, system or product. While carbon dioxide is the poster child for greenhouse gases, other such gases include methane, nitrous oxide and ozone (not to mention vaporized water or the condensed form, clouds). To create a standardized unit for greenhouse gas impacts all these varieties of emissions are converted into a carbon dioxide equivalent.

Reasonable, but this doesn't go far enough: why stop with carbon? There are several planet-wide systems that maintain life; climate change is but one of myriad ways human activity harms the planet. There's ecosystem destruction, dead lakes and ocean from acidification, loss of biodiversity, nitrogen and phosphorous cycles, dangers from particulate load in air, water and soil, pollution from man-made chemicals and more.

All these problems arise because virtually all human systems for energy, transportation, construction, industry and commerce are built on platforms that degrade those global systems. Calculating the overall ecological footprint of a given activity give us a more fine-tuned metric for the rate at which we are depleting all the global systems that sustain life on the planet—not just the carbon cycle.

Such metrics emerged from the relatively new science of industrial ecology, an amalgam of hard sciences like physics, chemistry and biology, with practical applications like industrial engineering and industrial design. This eco-math helps us perceive impacts we are otherwise oblivious to. For instance, when industrial ecologists measure how much of the carbon footprint you remediate when you recycle the plastic container for a yogurt, the result is about five percent of the yogurt's carbon footprint. Most of the yogurt's carbon footprint results from the methane emitted by digesting cattle, not from the plastic container.

Then there's the motivational problem. Evolution shaped the human brain to help our ancestors survive in an era when the salient threats were predators. Our perceptual system was not tuned to the macro and micro changes that signal threats to the planetary support system. When it comes to these threats we suffer from system blindness.

While footprints offer a cognitive workaround that can help us make decisions that favor the planet, they too often have an unfortunate psychological effect: Knowing the planetary damage we do can be depressing and demotivating. Negative messaging like this, research from fields like public health finds, leads many or most people to tune out. Better to give us something positive we can do than to shame or scare us.

Enter the "Handprint," the sum total of all the ways we lower our footprint. To calculate a handprint, take the footprint as the baseline, and then go a step further: assess the amount ameliorated by the good things we do: recycle, reuse, bike not drive. Convince other people to do likewise. Or invent a replacement for a high-footprint technology, like the sytrofoam subsititute made from rice hulls and mycelium rather than petroleum.

The handprint calculation applies the same methodology as for footprints, but reframes the total as a positive value: Keep growing your handprint and you are steadily reducing your negative impacts on the planet. Make your handprint bigger than your footprint and you are sustaining the planet, not damaging it.

And such a positive spin, motivational research tells us, will be more likely to keep people moving toward the target.